1. Field of the Invention
The present invention relates to a method and apparatus for forming an organic thin film on a substrate surface.
2. Description of the Related Art
In recent years, development of material techniques using organic molecules is remarkable. Along with the development, there is a strong tendency for realizing a new functional element using organic molecules. In particular, extensive studies for developing an element utilizing an ultra thin film using organic molecules have been made.
As a conventional method of forming an organic thin film, a spin-coating method, vacuum deposition method, Langmuir-Brodgett method, and the like are known. Of these methods, the Langmuir-Brodgett method is receiving a lot of attention as the sole thin film forming method with which organic molecules can be oriented and stacked in units of .ANG.. In the following description, the Langmuir-Brodgett method is abbreviated as an LB method, and a film formed by the LB method is referred to as an LB film. An example of an element to which the LB film may be applied includes a MIS light-emitting element and a MIS transistor having an LB film as an insulating film, a photoelectric transducer using pigment molecules, optical recording medium, and various sensors, a piezoelectric element using a polarity film structure, and the like. In addition, an attempt is made to use the LB film as an ultra micropatterning resist.
In the conventional LB method, amphiphilic molecules consisting of single molecules are developed on a water surface, and are compressed to a predetermined surface pressure to form a condensed film. Thereafter, a sample substrate is vertically moved to cross the monomolecular film, thereby building up an organic molecular thin film on the substrate. This method is called a vertical dipping method. In contrast to this, in another method, a sample substrate is brought into parallel contact with a developed monomolecular film, thereby attaching an organic molecular thin film on the substrate. This method is called a horizontal attaching method. The structure of built-up monomolecular film obtained by these methods includes a Y-type wherein hydrophilic group molecules are built up adjacent to each other, while the hydrophobic group molecules are built up adjacent to each other, and X- and Z-types wherein the hydrophobic group molecules are built up to be adjacent to those of the hydrophilic group. When the substrate surface has a hydrophilic property, a hydrophobic group side of a monomolecular film first attached serves as a substrate side, and the hydrophobic group molecules of the next monomolecular film are attached to the hydrophilic group molecules of the first monomolecular film. A built-up film in which the monomolecular films are built up in this manner is called the X-type. A built-up film in which hydrophilic and hydrophobic group molecules are sequentially built up to be adjacent to each other on a substrate surface having a hydrophobic property is called the Z-type.
However, when the monomolecular films are built up while the hydrophilic and hydrophobic group molecules are adjacent to each other, energy at an interface between these films becomes very large. For this reason, the X- and Z-type built-up films have unstable structures in view of energy, and tend to change over time. In order to obtain a good multilayered structure, a Y-type built-up film is effective in any building up method.
In general, in a manufacturing apparatus for manufacturing a monomolecular film, a substrate is held by a holder, and the holder is connected to a lift mechanism through an arm. For example, when a Y-type built-up film is formed on a substrate surface using the manufacturing apparatus, the substrate held on the holder is conveyed to a position above a monomolecular film developed on a liquid surface of a trough, and is dipped in the trough through the monomolecular film by the lift mechanism. In this case, the monomolecular film is attached to the substrate surface. The substrate is then pulled up from the trough through the monomolecular film, and a second monomolecular film layer is attached to the substrate surface.
However, in the manufacturing apparatus, when the substrate is pulled up from the trough, the arm located between the substrate and the lift mechanism passes through the developed monomolecular film prior to the substrate. When the arm passes through the monomolecular film, it may destroy the monomolecular film or change the surface pressure of the monomolecular film. Since the monomolecular film is attached to the substrate surface after the arm passed through the film, a film having high quality cannot be formed on the substrate surface.